This application claims the priority of German application 198 57 160.7, filed in Germany on Dec. 11, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for open-end spinning comprising an opening roller, a spinning rotor and a fiber feed channel for transporting fibers by means of a suction airflow from the opening roller to the spinning rotor, said fiber feed channel tapering in a fiber transport direction, having a deflecting zone on its transport path, and being provided, at a distance upstream from its narrowest cross section, with a bypass opening for drawing off a part of the suction airflow.
An apparatus of this type is prior art in U.S. Pat. No. 5,065,572. In the case of such an apparatus, the largest possible amount of suction airflow is desired, so that no disturbances in the fiber transport, nor any fly contamination in the area of the opening roller, can occur. The amount of air in the suction airflow is set, however, by the narrowest cross section, which as a rule is located at the exit opening, and determined also by the installed vacuum. For energy-saving reasons, the pressure differences are kept at a minimum. The narrowest cross section is, however, limited by the diameter of the spinning rotor, which diameter, at the current standard speeds of 130,000 rpm and more, lies clearly below 30 mm. Small exit openings result, however, as mentioned above, in fly contamination in the area of the opening roller.
By means of the bypass opening known from the above mentioned prior art, the suction cross section in the area of the opening roller can be enlarged, so that, despite a narrow diameter at the exit mouth of the fiber feed channel, a sufficiently large amount of air can be sucked in. A part of the suction air flow is already drawn off by means of the bypass opening before it reaches the narrowest cross section. As the bypass opening is disposed in transport direction downstream of the deflecting zone in the case of the known apparatus, the aim is to prevent any fibers being drawn off with the air through the bypass opening, and that all fibers reach the exit opening and thus are disposed in the spinning rotor. It has been shown, however, that a part of the fibers are drawn off with the outgoing air through the bypass opening.
It is an object of the present invention to avoid the disadvantages present in the embodiment of the above mentioned apparatus and to ensure that, while maintaining the advantages of the known bypass opening, no fibers are prematurely drawn off, but rather that all fibers reach the spinning rotor.
This object has been achieved in accordance with the present invention in that the bypass opening is arranged immediately after the beginning of the deflecting zone, in an area which is substantially free of fibers.
The present invention is based on the knowledge that the inertia of the fibers in the suction airflow is so great that the fibers require a distance, even if only a short one, downstream of the deflecting zone until they are distributed over the whole cross-section of the fiber feed channel. If the bypass opening is arranged immediately after the beginning of the deflecting zone, said bypass opening being preferably the entry opening of the outgoing air duct, which is directed in the opposite direction to the transport direction of the fiber feed channel, it can then be presumed that all fibers are guided past the bypass opening without being drawn off in an undesired way.
Often fiber feed channels are made up of several channel sections, for example when the area of the exit opening is arranged in a separate adapter, which is adapted to the particular dimensions of a spinning rotor. In an advantageous embodiment of the present invention, the fiber feed channel consists thus of two channel sections, having at the deflecting zone a partition seam, at which the bypass opening is located. In this way, the deflecting zone can be constructed in a technically practical way, whereby the fiber feed channel, as a rule, is bent at the deflecting zone.
It is favorable when the exit opening of the fiber feed channel and the bypass opening are both connected to a joint vacuum source. This can be the vacuum source to which the spinning rotor is connected anyway for the generation of the necessary suction airflow.
As mentioned above, a sufficiently large amount of air should be present in the area of the opening roller. The in-going air in this area is fed usually through a trash removal opening located on the periphery of the opening roller. Exactly at this point, however, it is not desirable to have too high a suction airflow speed, so that the removal of light trash particles is not impeded. It is known from U.S. Pat. No. 5,809,766 that the air speed at the trash removal opening is effectively reduced in that downstream of the trash removal opening, but at a significant distance from the start of the fiber feed channel, an additional inlet air opening is provided. This additional opening, in a further embodiment of the present invention, can be a bypass air inlet opening which supports the suction airflow. Thus the amount of air is increased in a desired way there where the fibers are released from the opening roller and enter into the fiber feed channel, without, if a trash removal opening is present, the air speed being too greatly increased at this point. This so-called double bypass results, as has been shown, in a favorable balance of air streams in the fiber feed channel.